The copending application, Ser. No. 048,166, filed June 13, 1979 of Dholakia entitled "Method for Precision Grinding of Sharp Tips," is being filed concurrently with the instant application. Dholakia discloses that a thick, abrasive silicon oxide layer can be used to lap the narrow, sharp point of a hard material such as diamond, sapphire and the like to a flat surface with a smooth finish. The Dholakia method both results in reduced breakage of the tips during lapping and prevents destruction of the lapping medium.
Several problems were encountered in the initial attempts to prepare thick SiO.sub.x abrasive layers by employing a glow discharge. SiO.sub.x may be thought of as a mixture of SiO.sub.2 and SiO. The vinyl substrate, which is a preferred substrate, should not be heated above a temperature of about 50.degree. C. Above this temperature the vinyl may warp due to stress relaxation which limits the disc's usefulness. This temperature sensitivity limits the maximum time the substrate may reside in the glow discharge. The maximum coating thickness which may be deposited for a given deposition rate is limited by the residence time. Several deposition steps, allowing the substrate to cool between them, are often required to produce a coating having the desired thickness.
SiO.sub.x layers may be glow discharge deposited using silane or certain of its derivatives as precursors. When organosilane precursors such as methyldimethoxysilane and tetraethoxysilane are employed, difficulties arise in the deposition of thick abrasive layers because of the reactivity of the organosilanes in the absence of the glow discharge plasma. These precursors condense to form thin amorphous films on the substrate in the presence of residual water or oxygen via hydrolysis or oxidation, respectively. The condensed materials adhere poorly to the substrate and cause coating inhomogeneity when they deposit on the intermediate layers between deposition cycles. Thus, in practice it is difficult to deposit a thick film by simply repeating the deposition at the time intervals set by the thermal sensitivity of the substrate in order to avoid the problem of excessive heating discussed above.